The present invention relates to a data transmission system, more particularly, to a data transmission system capable of transmitting a variety of data between each of a plurality of terminal units which transmit and receive such data via a plurality of transmission lines connected thereto.
When a plurality of terminal units are connected to a transmission line while data transmission is performed between two of them, a certain signal is given to the remaining terminal units, informing them that the data transmission line is engaged, and as a result, except for these two units, no request for using the transmission line can be generated by the remaining units.
Conversely, if a plurality of terminal units simultaneously request any available transmission line and permission for using a transmission line is simultaneously given to a plurality of terminal units, it will result in a confusion in transmitting a variety of data, causing them to be incorrectly transmitted. To prevent this, conventional data transmitters apply means, which, on request of any terminal unit for using a transmission line and upon detecting an additional request for any available transmission line from another terminal unit at the same time, allows the controller to output an encoded bit sequence signal so that the terminal unit requesting the line can detect the presence of such an additional request (hereinafter such a request is referred to as a collision), thus resulting in the improved capability for correctly detecting such a collision in the transmission line. Nevertheless, with any of the conventional data transmitters, a complex circuitry has to be used for properly generating such a bit sequence signal, and in addition, due to a need for providing a software operation circuit, as a whole, such conventional data transmission systems are found disadvantageous for use with their complex structures and due to relatively higher cost.